World

Why This Winter Storm Blows Other 2014 Storms Away

NOAA satellite image of the winter storm moving up the East Coast on Feb. 13, 2014.

Image: NOAA

By Andrew Freedman2014-02-13 16:08:53 UTC

The snow and ice storm slamming the eastern seaboard is not like the other storms so far this busy winter. It is far more intense, more expansive, and more impactful than the others, unleashing a wide variety of hazardous weather conditions that have already proven deadly.

Unlike the snowstorms that have struck the East Coast so far this winter, which have mainly featured heavy snow and frigid temperatures, this storm is more of a classic nor'easter. As with many things in life, the storm required a combination of things to come together at just the right time in order for it to happen.

First, there was energy in the form of atmospheric spin embedded in the jet stream, which is a river of high speed air flowing at airliner cruising altitudes. This spin moved southeast toward Alabama at the same time that a series of surface low pressure systems formed near the Gulf Coast, drawing copious amounts of Gulf of Mexico moisture northward. Once the upper level energy caught up to the surface low, the overall storm intensified rapidly.

The other crucial ingredient was a firmly entrenched area of cold, dense air that hugged the ground. This forced the milder, moist air from the Gulf to flow up and over the cold air, which is a classic recipe for a wintry mix of precipitation.

The result? A mess of ice, sleet, snow, and even severe thunderstorms. Because of the ice damage and disruption to economic activity in major East Coast cities, it is likely that this storm will be a billion dollar disaster in the U.S.

The ice proved to be extremely destructive, although not quite as bad as feared in the Atlanta metro area, where colder-than-expected temperatures led to more sleet mixing in with the freezing rain.

In the South, the storm coated trees and power lines with ice up to an inch thick, and a whopping 3 inches of sleet in Forest Acres, S.C. While major ice storms have occurred in the South in the past, ones this severe are a rarity.

According to the National Weather Service (NWS), the ice storm winner (or loser, considering the adverse consequences) was Orangeburg, South Carolina, where an inch of ice was recorded. An inch of ice was also observed in northern Louisiana.

Other locations in the Palmetto State had 0.75 inches of ice, which was more than enough to knock down trees and power lines. News reports said more than 500,000 people were without power across the South, and outages may continue for days as crews work through the tangled mess of wires and tree limbs.

As the upper level low dug in behind the surface low pressure center, thundersnow was reported in the Birmingham, Alabama area, where up to 6 inches of snow fell. The jackpot in Alabama was the city of Cullman, about 50 miles north of Birmingham, where 10 inches fell.

While the storm slightly underperformed when it came to ice, it has made up for it with unexpectedly heavy snowfall. On Thursday, there were reports of more than a foot of snow having already fallen west of Washington, D.C. and Baltimore, with the possibility of at least another foot as the storm consolidates its energy off the Atlantic coast, and pulls in more moisture off the ocean.

As of early Thursday morning, 13 inches of snow had already fallen in Laurel Ridge, Virginia, and 9 inches in Roanoke. Many meteorologists spent Thursday morning raising snowfall totals for areas west of the I-95 corridor, as computer model simulations show a second round of heavy snow moving into the Washington to Boston corridor on Thursday night. During the first round, New York City picked up a whopping 7 inches of snow in just 3 hours.

The heaviest snow overnight and into Thursday morning occurred in a region that meteorologists call a "baroclinic leaf." This region lies underneath what appears to be a comma head on satellite imagery. A baroclinic leaf occurs when low pressure systems are forming and intensifying. They are located in a region of a storm where the air is rising rapidly, as a conveyer belt of relatively mild and moist air feeds into the storm, and upper level winds diverge, forcing air at lower levels to rise. This rising motion causes air to cool and condense, eventually forming clouds and precipitation.

Other mechanisms will result in an expanding shield of snow that will move northward into New England on Thursday. In a heavy snowfall discussion on Thursday morning, the NWS said the low pressure center forming along the North Carolina coastline is likely to strengthen rapidly, undergoing a process known as "bombogenesis." The formal definition of bombogensis is when a storm's central air pressure plunges at least 24 millibars in 24 hours. The current storm is predicted to drop at least 25 millibars in 24 hours. In general, the lower the air pressure is, the stronger the storm.

The Weather Channel reported that a dozen deaths have a occurred so far because of the storm, five of which were from traffic accidents in Alabama.

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